1. Field of the Invention
The present invention relates to an actuation device for a friction clutch arranged in the drivetrain of a motor vehicle between a drive unit and a transmission arrangement, the actuation device having a pressure medium force cylinder arrangement for actuating the friction clutch via a release member having a release bearing arrangement, a measuring arrangement for detecting an actual release and/or instantaneous release member position, and a control/regulating valve arrangement connected with a pressure medium source, a pressure compensation opening or a pressure compensation reservoir and the pressure medium force cylinder arrangement, the control/regulating valve arrangement arranged for actuating the pressure medium force cylinder arrangement in response to the actual release or the instantaneous release member position and on a reference release which may be predetermined.
2. Description of the Related Art
An actuation device for a friction clutch including a pressure medium force cylinder arrangement for actuating the friction clutch via a release member having a release bearing arrangement and a control/regulating valve arrangement arranged for actuating the pressure medium force cylinder arrangement is known, for example, from German reference DE 197 16 600 A1, whose disclosure is incorporated in the disclosure of the present application by reference.
With regard to the service life of drivetrains, especially in utility motor vehicles, the release bearing arrangement of the actuation device for actuating the clutch is increasingly regarded as the weakest link in the drivetrain. The life of the drivetrain is an important competitive feature for automobile manufacturers and their suppliers. It would be ideal if all components would last as long as the engine, for example, 800,000 to 1 million kilometers based on conditions prevailing in Europe. With respect to conditions in the USA, a life of more than 1 million kilometers may even be assumed.
With respect to labor costs and immobilization periods of the vehicles, the mileage up to the first engine/transmission disassembly plays an important role. Until recently, clutch facings typically had to be replaced at least once during the life of the engine because of comparatively high facing wear. When the clutch facings were replaced, the relatively inexpensive release bearing was also changed as a precaution, so that it was not until recently that any attention was paid to release bearings and the release bearings were generally constructed without sealing in spite of unfavorable operating conditions (for example, temperature and dust) and release bearings generally did not require premature repair or maintenance steps. As was also the case previously, this situation still applies to distribution vehicles and construction site vehicles in which interim replacement of facings and advisably also of release bearings is still required and practiced today. However, in long-distance transport vehicles, the clutches including the clutch facings are increasingly able to last just as long as the engine. Accordingly, the life of the release bearing is now a factor. To increase the life of the release bearing, its sealing was improved and openings provided in the clutch covers were closed insofar as practicable. However, these solutions still did not produce adequate results.
The object of the present invention is to improve the life of the release bearing for friction clutches. To meet this object, the actuation device is adjustable or displaceable in a defined manner between a non-actuation state and an actuation state according to the present invention, wherein the release bearing arrangement is decoupled from an associated release force receiving arrangement of the friction clutch in the non-actuation state and is coupled with the release force receiving arrangement in the actuation state. The release force receiving arrangement may comprise an engagement spring arrangement.
The present invention is based on the idea and insight that the friction clutches in vehicles used in long-distance transport only run about 100 to 200 hours total operating time in the fully or partially released state. It is only during this time that the release bearing transmits the release force used for clutch actuation. During the rest of the operating time, the release bearing generally rotates at the rotational speed of the crankshaft with a preloading of approximately 2 to 3% of the maximum release force.
Assuming an engine life of about 15,000 hours in engines with more than 10 liters piston capacity (in long-distance transport, this life corresponds approximately to a traveled distance of 900,000 km assuming an average speed of 60 km, while the distance is correspondingly shorter in distribution and construction site transport because of the lower average speed), the total releasing time is about 1% of the operating period. Accordingly, the release bearing idles for 99% of the operating period and transmits engine vibrations to the release system. In Class 8 vehicles in the USA, there is an even greater incongruity between clutch transmission and idle time of the release bearing because shifting occurs without clutch actuation in this class of vehicle. The clutch is needed only for startup and shifting. Therefore, a total force transmission duration of about only 50 hours may be assumed for the Class 8 vehicles.
In this connection, the construction of the actuation device according to the present invention makes an extraordinary increase in the life of the release bearing arrangement possible. For operating periods in which the clutch is not to be actuated or in which there is no pending clutch actuation, the actuation device may be adjusted to the non-actuation state in which the release bearing arrangement is decoupled from the release force receiving arrangement with a corresponding gentler treatment of the release bearing arrangement. The actuation device only needs to be moved into the actuation state for clutch actuation and possibly for expected clutch actuation to couple the release bearing arrangement with the release force receiving arrangement. In short, the construction of the actuation device according to the invention allows the release bearing arrangement to run only when it is actually used or when clutch actuation is imminent. Consequently, the release bearing arrangement is exposed to less wear and is therefore more reliable and has a longer life.
Furthermore, the increased reliability and life of the release bearing arrangement which is achieved according to the present invention allows less complicated and therefore economical release bearing components to be used.
In addition to the advantage of increased life and the resulting increased dependability of the release bearing arrangement, the direct transmission of engine vibrations to the release system is eliminated or at least greatly reduced by adjusting the actuation device to the non-actuation state. The pressure medium force cylinder arrangement may, for example, include a pneumatic force cylinder arrangement or a pneumatic ring cylinder. Micromovements of the pressure medium force cylinder induced by engine vibrations contribute to wear of the seals acting between the pressure medium piston and cylinder. Accordingly, an increased life of the seals and accordingly a prolonging of the maintenance-free operating period of the pressure medium force cylinder arrangement is achieved by reducing or eliminating micromovements of the pressure medium force cylinder arrangement deriving from microvibrations.
However, providing a non-actuation state to which the actuation device may be adjusted requires changing the typical actuation device which may forfeit some advantages of the known actuation device. For example, the adjustment of the actuation device from the non-actuation state to the actuation state requires a certain time. Accordingly, a construction of the actuation device according to the present invention introduces a time constant which limits the reaction or response time of the actuation device, at least when no special additional steps are taken to at least make up for this time constant. When the non-actuation state is realized through the introduction of play or dead travel, the release path portion of the total clutch pedal travel is reduced by the amount of play or dead travel when the non-actuation state is introduced which increases the level of force required for release. For this reason, known hydraulic clutch actuation devices are constructed with no play in the clutch actuation system. Moreover, known clutch pedals actuating a hydraulic master cylinder always occupy a position independent from facing wear because of wear compensation that is achieved via a blow bore hole in the master cylinder. Furthermore, doing away with an idle path caused by play in the known clutch actuation devices results in a favorable pedal characteristic at a low level of pedal force.
According to a further embodiment of the present invention, the actuation device may be adjusted to an actuation-ready state in which the release bearing arrangement is coupled with the release force receiving arrangement in the engaged position of the clutch or is proximate the release force receiving arrangement in the engaged position of the clutch so that the release bearing arrangement may be coupled with the release force receiving arrangement with a slight adjustment. According to this further embodiment, the actuation device may be adjusted to the actuation-ready state when a clutch actuation is pending or at least prognosticated. The time constant ascribed to the actuation device for clutch actuation proceeding from the actuation-ready state is substantially smaller than the time constant attributed to a clutch actuation proceeding from the non-actuation state. In this further development, short response times are achieved as is required, for example, for split shifting operations in split-range transmissions.
The actuation state, the non-actuation state and the optional actuation-ready state may be defined in different ways. For example, the actuation state may be defined as when the release bearing arrangement in the actuation state transmits a release force between the release member (such as a release piston of the pressure medium force cylinder arrangement) and the release force receiving arrangement. The non-actuation state may be defined as when the release bearing arrangement in the non-actuation state does not transmit any substantial releasing force or preloading force between the release member and the release force receiving arrangement. The actuation-ready state may be defined as when the release bearing arrangement in the actuation-ready state is coupled with the release force receiving arrangement and a preloading force is transmitted between the release member and the release force receiving arrangement.
The release bearing arrangement may comprise a first bearing part which is rotatable along with the clutch and a second bearing part arranged at the release member so as to be fixed with respect to rotation relative to the release member. In this embodiment of the release bearing arrangement, the actuation state may be defined as when a rotational driving connection is produced between the clutch and the first bearing part via the release force receiving arrangement and the non-actuation state may be defined as when this rotational driving connection is interrupted. The actuation-ready state may be defined as when the release bearing arrangement is coupled with the release force receiving arrangement and the rotational driving connection is produced between the clutch and the first bearing part by the release force receiving arrangement.
The non-actuation state may be realized in a simple manner by introducing an idle path in the release system such that the release bearing arrangement occupies a standby or waiting position in the non-actuation state which is displaced by the idle path relative to an operating position corresponding to a completely engaged state of the friction clutch. In this case, the release bearing arrangement in the actuation-ready state, insofar as it is provided, may occupy a ready position which substantially corresponds to the completely engaged state of the friction clutch.
An adjusting spring arrangement which biases in the direction of the waiting position may be provided. The release bearing arrangement may be moved into the waiting position by this adjusting spring arrangement. An adjusting spring arrangement of this kind is particularly relevant when the pressure medium force cylinder arrangement comprises a single-action arrangement in which, because of the idle path, the release force receiving arrangement (which may, for example, be an engaging spring arrangement such as diaphragm spring arrangement) is not available to move the release bearing arrangement into the waiting position.
However, the release bearing arrangement may be moved into the waiting position via the pressure medium force cylinder arrangement if the pressure medium force cylinder comprises a double-acting arrangement.
A mechanical stop may be used to define the waiting position. The mechanical stop generally defines a wear-independent waiting position, so that the idle path changes in response to clutch wear insofar as appropriate steps for wear compensation are not taken.
The waiting position may vary according to the state of wear of the friction clutch to provide a constant idle path. For example, it may be desirous to provide a very short idle path (a small defined play) independent from the instantaneous wear state to ensure short, wear-independent actuation times. The waiting position may be adjusted and maintained, for example, completely independent from a mechanical stop via the pressure medium force cylinder arrangement by regulating/controlling the position by pressure medium (for example, pneumatic position regulation/control or hydraulic position regulation/control). In this embodiment, the force of an optional adjusting spring or restoring spring arrangement may be held in equilibrium by the pressure medium pressure.
With regard to holding the release bearing arrangement in the waiting position in the non-actuation state, the release bearing arrangement may be held in the waiting position in the non-actuation state by the pressure medium force cylinder arrangement and/or by the adjusting spring arrangement and/or by friction forces.
The actuation device further includes a control/regulating unit which adjusts the actuation device, as required, between the non-actuation state and the actuation state or between the non-actuation state, the actuation-ready state and the actuation state. In response to the actual release state which is determined relative to the instantaneous release member position and a desired release state, the control/regulating unit actuates the pressure medium force cylinder arrangement in the actuation state via the control/regulating valve arrangement to actuate the clutch. The desired release state may be a default valve or a value based on empinical data. In this way, the actuation device may acheive very short effective actuation times which even satisfy the very high requirements of split shifting in this respect. Accordingly, an adjusting strategy realized by the control/regulating unit may be provided in that the actuation device is adjusted to the actuation-ready state and is left in this state so that the release bearing arrangement continuously runs along with the friction clutch in the lower gears of the transmission arrangement in which the shifting processes generally succeed one another quickly. The actuation device may be adjusted to the non-actuation state in the upper gears so that the release bearing arrangement does not run along with the friction clutch and is consequently treated with care. The adjustment of the actuation device between the different states by the control/regulating device may be performed in response to information which, for example, is supplied by a driving speed signal and/or a shift group signal of the transmission arrangement to the control/regulating unit.
The control/regulating unit acts on or influences the actuation device i.e., the state occupied by the actuation device, via the control/regulating valve arrangement and the pressure medium force cylinder arrangement. In this respect, it is noted particularly that the control/regulating unit actuates the pressure medium force cylinder arrangement via the control/regulating valve arrangement for adjusting the actuation device from the non-actuation state into the actuation-ready state or from the non-actuation state through the actuation-ready state to the actuation state or from the non-actuation state into a boundary state belonging to the actuation state of beginning clutch actuation or from the non-actuation state through the boundary state into the actuation state.
The boundary state is the state between the non-actuation state and the actuation state. In the boundary state, the release bearing arrangement may momentarily occupy a boundary position which essentially corresponds to the fully engaged state of the friction clutch. In a corresponding manner, the release bearing arrangement in the actuation-ready state mayxe2x80x94as was already mentionedxe2x80x94occupy a ready position which essentially corresponds to the fully engaged state of the friction clutch.
In general, the adjustment of the actuation device between the states (actuation state, non-actuation state and possibly actuation-ready state) and the clutch actuation itself may be based on boundary position information and ready position information which is either predetermined or detected. The detection of the position information may include using the control/regulating unit to determine the ready position and boundary position based on measurements taken by the measuring arrangement and storing the measurements for use in further operation.
The control/regulating unit may determine the ready position and the boundary position from a change in an adjusting speed of the release member which occurs when moving through the ready position or boundary position. This determination is preferably made during an adjustment of the actuation device between the non-actuation state, the actuation-ready state or boundary state, and the actuation state. Accordingly, the control/regulating unit may identify the ready position or boundary position as a position of the release member, i.e., the release bearing arrangement, in which the adjusting movement of the release member is braked in a defined manner by the engagement spring arrangement in the course of a disengagement by the adjustment of the actuation device from the non-actuation state to the actuation state.
The control/regulating unit may also identify the ready position or boundary position as a position of the release member which corresponds to a relaxed engagement spring arrangement and the position to which the engagement spring arrangement adjusts the release member, including the release bearing arrangement, in the course of a complete engagement. For example, the conclusion of the engagement process, namely, the relaxation of the release spring arrangement (possibly the diaphragm spring arrangement) may be utilized in that the measuring arrangement detects the position in which the release bearing arrangement or the clutch release (possibly actuation piston) is adjusted by the release spring arrangement.
The control/regulating unit may optionally comprise a prognostic unit which forecasts the frequency and/or probability of future clutch actuations (clutch release processes) in a preview time interval based on operating and/or driving states of the vehicle, operating and/or actuation states of the transmission, operating states of the drive unit, and/or actions of a driver. The control/regulating unit optionally adjusts the actuation device between the non-actuation state and the actuation-ready state depending on the prognosis. The prognostic unit forecasts the frequency and/or probability of future clutch actuations in a preview time interval and accordingly allows the adjustment of the actuation device in response to (1) the instantaneous requirements for switching between the above-mentioned states and (2) the future needs to switch between the states. As was already indicated above, a reduction in the effective time constant of the actuation device with respect to carrying out clutch actuations may be achieved in this way. Moreover, this embodiment avoids the need to constantly adjust the actuation device between the above-mentioned states successively in short time intervals with resulting frequent acceleration of the release bearing arrangement from a standstill, at least under normal driving and operating conditions forming the basis of the prognosis. With respect to acceleration processes, wear on the release bearing deriving from acceleration of the release bearing from a standstill to clutch speed and/or noises deriving from these acceleration processes is appreciably reduced by use of the prognostic unit.
As was already mentioned, the pressure medium force cylinder arrangement may comprise a pneumatic force cylinder arrangement. Further, the control/regulating valve arrangement may comprise an electrically controlled valve arrangement.
The present invention is directed to a motor vehicle drivetrain, particularly a drivetrain in a utility vehicle, comprising a drive unit, i.e., an internal combustion engine, a transmission arrangement and a friction clutch arranged between the drive unit and the transmission arrangement, and comprising an actuation device according to the present invention. The transmission arrangement may be a transmission arrangement of the type which can be shifted regularly without clutch actuation such as, for example, class 8 vehicles in the USA, ASG design, or the Opticruise type. However, the transmission arrangement may also be the type that can be shifted regularly at least between determined gear multiplications only by clutch actuation such as, for example, a split-range transmission for which short clutch actuation times are generally required.
The invention is described more fully in the following with reference to embodiment examples shown in the Figures, wherein identical reference numbers are used for analogous or corresponding or identical structural component parts and functional elements.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.